The best way to help is revision...revision...and more revision. Also, ask your teacher to go over topics you're really confused on- sometimes things are a lot clearer when they're doing 1 to 1 teaching. YouTube is awesome for finding videos to take you through concepts and methods- just type in something like "GCSE atom structure" and loads will come up. TylerDeWitte is a really good science channel, I know they do AS stuff but they might do GCSE as well.
There are also some really good revision guides- CGP gives outlines and practive questions on everything in your course. Use past papers as well, because exam technique is really important expecially in questions where you need to explain or show a concept. Hope this helps a little x